Let me send ahead that this isn't supposed to be a pretty picture presentation but rather a report of the startup of the new RC8 that I bought recently. Hence, I haven't collected data under the very prefect circumstances. The focus here was to assess the optical quality, dial it in if necessary and see how strong the remaining aberrations are. Maybe somebody can find this information helpful in the setup of his new scope.

So, what happened? I've sold my Meade 8" ACF and wanted to replace it with another scope. It had to be something that's certainly seeing and not diffraction limited.
The 105mm f/7 APO that I have is just at the boundary. With my ASI294MM at 2x2, the diffraction limit and image scale match at approximately 1.2"pp. For my typical seeing conditions, this setup is kind of a sweet spot. 

What scope next? Well, resolution wise, it might be questionable how much I would gain if I achieve an image scale of 0.4"pp. There might be rare nights where this could be helpful but most of the time, it won't help. It's more aperture and hence light gathering capability that I wanted. Certainly, aperture can only be replaced by more aperture but at some point this will lead to the next investment: a new mount, which isn't an option at this point of time.
The maximum aperture that seems reasonable for my CEM40 without the worry of approaching the weight limit seemed to be 8in reflectors. Apertures of 10"+ are close to 10kg or even more. The rated weight of my mount is 18kg but who knows how much share the engineering got and how much the marketing. 

I chose the GSO-based RC8 since I was hoping to run a reflector-only system with the major monochromatic aberrations corrected (namely coma and spherical aberration). As many may know, RC secondary mirrors are tricky as convex hyperboles are said to be difficult to manufacture and measure. Yet, a lot of people place a lot of good images here and so if quality is on a steady level, it might be worth the shot.

Said, ordered, arrived, unpacked and then first step: assessment of the parts and optical adjustment.

A very good investment is a tilt adapter for the focuser. Otherwise, I'd claim that an excellent optical alignment isn't possible.
Due to the large back focus, one will also need to use one or more spacer rings (came with the scope). In my case, I used the longest (50mm) and one of the shorter ones (I think it's 25mm. Didn't measure it as the focuser compensates for the missing distance). 

Next step: checking if the optics is correctly adjusted. Due to the strange design of the focuser, you can be certain that one has lost adjustment once the M90 ring of the focuser was opened. It's got a cone that's pressed against the M90 extension rings. Therefore, checking the alignment was more about: how bad has it become? Alignment will be necessary in either case.

For the centering and alignment procedure, I've tried to use a very simple approach and see how it goes. I'm using a collimation laser and a Cheshire eyepiece. Both of them are usually used for the alignment of Newton designs. Yet, it should also work with an RC. The last word as usual has the real star. Fortunately, I can place a self-made artificial star at around 15x FL and it helps me to collimate the scope.

What I've noticed from the very beginning is that the back focus of the OTA was at 270mm. That made me scratch my head since the specification mentions 254mm. Some internet research confirmed this number. Also, my first initial subs that I had captured have shown some drop shaped stars in the field's center. `To me this was an indicator that something must be certainly wrong. Doing some raytracing simulations, it turned out that there's a big difference in image quality if back focus is changed from 270mm to 254mm. Therefore, I've chosen to change the mirror spacing to achieve the specified back focus.

...continued in PARTII: M39, Testing the new GSO RC8 telescope PART II

A few words about the image:
The above image is the result of two short imaging sessions. I haven't been focusing on excellent post-processing but on the star shapes over the field. Therefore, the image is only cropped down to the intersecting area of all the subs (I'm using dithering. Otherwise the integration shows too much fixed pattern noise.).

It was captured with the correctly adjusted optics (BF=254mm) and without flattener.

Or course, feel free to comment!